Japanese utility model laid open patent publication No. 68627/1980, which is published on May 12, 1980, discloses a device for controlling a throttle valve including a cruise controller and accelerator pedal. According to this conventional device, the throttle valve is controlled by the accelerator pedal and the cruise controller.
Accordingly, when the cruise controller is operated, the throttle valve is automatically controlled by the cruise controller without an operation of the accelerator pedal. Further, the throttle valve is opened from a position demanded by the cruise controller if the accelerator pedal is depressed largely. That means the throttle valve is located maximum opening position demanded by the accelerator pedal and the cruise controller.
By the way, it is not preferable for the vehicle to increase an engine power when the vehicle runs on an iced field. Because a needless engine power decreases a friction grip (friction force) between vehicle wheels and the iced field, and then, decreases a stabilization for a vehicle running.
Accordingly, it is preferable for the vehicle to decrease the needless engine power when the vehicle runs on the iced field. By decreasing the needless engine power, a difference between vehicle velocity and wheel speed is reduced and the friction grip is increased. Such control for engine power is called "traction control".
However, the conventional device for controlling the throttle valve can not close the throttle valve from the position demanded by the accelerator pedal. Therefore, if the needless engine power is demanded by the accelerator pedal, there are no way to reduce the needless engine power.